backfiring through rebuilt 97 Strombergs

[burly]

Guys, I've got the Dual Carb set-up idling and accelerating well other than a fairly routine slight hesitation and backfire through carburetors when I shift from 1st into 2nd gear? Warm or cold. Didn't do that with single intake and carb. Fresh stock build 24 stud, bubba's rebuilt crab dizzy, new 6v coil, wires and plugs. Appreciate any suggestions you'd be willing to share. Thanks!